Processors may have several calibrating devices that need calibration using external devices. For example, for each type of input-output (IO) transmitter having an on-die termination, a replica circuit with its own external resistor is used to calibrate the on-die termination in the replica circuit according to the external resistor. This calibrated on-die termination is then used to set the on-die termination for the IO transmitters. If there are ten different types of IO transmitters, then ten different external resistors are used for calibrating the on-die resistances of the ten different replica IO transmitters. For each external resistor, a separate pin is required. In some cases more than one pin is used per external reference device. These additional pins increase cost of the processor and also add complexity to routing in motherboards.